The present invention relates to towing methods and installation methods for deepwater pipelines and steel catenary risers (SCR).
The history of pulling and towing pipelines on the seabed for the petroleum and waste water disposal industries dates back to the late 1940s. Since high power tow vessels were not available, most of the early deepwater pipeline systems were pulled using anchored barges. As higher power tow vessels were developed, the dynamic towing of pipelines became feasible, and several dynamic towing and installation methods were developed, such as, for example, the methods commonly known as the “S-lay” method and the “J-lay” method. The towing and installation of heavy, deepwater SCRs and pipelines by these conventional methods are often risky and expensive, and they are subject to water depth limitations, and they have not been feasible (for technical and/or economic reasons) for installation depths much greater than about 2500 meters.
As greater installation depths are being considered (e.g. 1800 to 2700 meters), the total submerged weight of the pipeline must drastically increase, due to, for example, the need for greater wall thicknesses for the pipe that are often necessary at extreme depths to avoid collapse and to maintain structural integrity and installation stability. There is a lack of surface equipment capable of handling such heavy pipelines using conventional towing and installation methods. Furthermore, very large offshore spreads are required to handle the installation of such massive pipelines. Thus, there still exists a need for a novel approach to deepwater pipeline towing and installation that can be used economically for very heavy deepwater pipelines.